Hmm… following the principle of least change, perhaps we could modify the tinker escort quest reward to give the player a device that creates a portal to the Steam Quarry (or perhaps teleports the player there itself)?
[Now, bear in mind that coding and testing this may take a while — not least because the last time I tried Infinite Dungeon was a pre-1.0 beta version. And because I keep EoR turned off for non-tinker characters, so I've never actually encountered the tinker escort. And because the Steam Quarry apparently has a min level of 30. So, yeah. Any recommendations for a good race/class for Infinite Dungeon?